Further thoughts - I don't want to pick on you particularly JMac, but your post is revealing:
Originally posted by JMac
. . . tuning the buffer cache hit ratio . . . .
. . . . what should we look for when tuning memory?
I think this emphasises how easy it is to get away from the real objective. I don't want to do either of the above, I want to "maximise throughput" or "minimise response time" or something similar which relates to business efficiency. No user will congratulate you on keeping the hit ratio above 95%!

Frankly, I didn't realise 100% what I was doing when I looked at "I/O Work" in my previous. Almost by accident I stumbled upon a rule which says: if you are going to look at hit ratios or parse/execute ratios etc, you'd be advised to write down some kind of short-hand which relates them to your real objective.
(Climbs down off soap-box.)